Polyvinyl halide (inclusive of vinyl halide homopolymers as well as copolymers of vinyl halide with up to about fifty percent of olefinic comonomer copolymerizable with the vinyl halide) is a widely used thermoplastic having a number of favorable technological properties. However polyvinyl halide, e.g. vinyl chloride homopolymer, breaks on impact very easily at ambient temperature and at still lower or sub-ambient temperatures. Thus at ambient temperature, i.e. at about 20.degree. C., corresponding to about 68.degree. F., the notched Izod impact resistance of the aforementioned vinyl halide homo- and copolymers is only of the order of about 0.4 to less than about 1 ft-lb./in. At sub-ambient temperatures, e.g. down to -20.degree. F. or lower, the notched Izod impact resistance of these polymers becomes vanishingly small or negligible. Generally the ambient temperature impact resistance of conventional vinyl halide polymers is enhanced by mechanically blending the vinyl halide with a minor proportion, i.e. less than 50%, of an impact enhancing elastomer additive, such as a methyl methacrylate-1,3-butadiene-styrene graft polymer, conventionally termed a polyvinyl halide impact modifier. The aforementioned impact modifiers moderately enhance the ambient temperature impact resistance of vinyl halide polymers, i.e. generally raise the ambient temperature notched Izod impact resistance of the polymer to about 2 to 10 ft-lbs/in. However, these impact modifiers are relatively ineffective in imparting a satisfactory sub-ambient temperature impact resistance to the polymer, i.e. the -20.degree. F. notched Izod impact resistance of the polymer containing the impact modifier is well below 1 ft-lb./in. and usually is about 0.4 to 0.5 ft-lb/in.
It has been discovered that polymerization of vinyl halide (or a monomer mixture of vinyl halide and copolymerizable ethylenically unsaturated comonomers) in the presence of a hydrocarbon polyolefin elastomer results in a polymer product (a vinyl halide-graft-polyolefin polymer) which contains vinyl halide polymer chains bound, i.e. grafted, at random points along the chain of the trunk olefin polymer as well as ungrafted vinyl halide polymer. The graft polymer product, especially the graft polymer product prepared by a liquid phase bulk polymerization reaction, has a substantially enhanced impact resistance at both ambient temperature and sub-ambient temperatures compared to the aforementioned conventional, i.e. ungrafted, vinyl halide polymers even when the latter are blended with a conventional polyvinyl halide impact modifying polymer additive. The bulk polymerization-prepared graft polymer product is even distinguished from the corresponding graft polymer prepared by a non-bulk polymerization technique, e.g. suspension polymerization, by an enhanced impact resistance at both low and ambient temperature and by breakage by the desirable ductile breakage mode rather than by an undesirable brittle breakage mode.
Although the aforementioned graft polymer possesses a subambient low temperature impact resistance substantially greater than that of conventional impact modifier-containing vinyl halide polymer compositions, the low temperature impact resistance of the graft polymer is found to decrease on ageing. Thus, for example, a molded article of the graft polymer, on ageing at ambient temperature for about one month or longer (or at an elevated temperature for proportionally shorter periods), tends to lose a significant amount, e.g. up to 35%, of its original high low temperature impact resistance. This loss of low temperature impact resistance on ageing is a particularly serious disadvantage when the graft polymer is employed in outdoor applications in a temperate climate wherein sub-ambient temperatures of the order 0.degree. F. to -20.degree. F. or even lower are often encountered during winter months (subsequent to summer months wherein the graft polymer is subjected to relatively high temperatures, e.g. of the order of 80.degree.-100.degree. F. or even higher, which serve to accelerate the ageing loss of low temperature impact resistance).
The foregoing problem of loss of low temperature impact resistance on ageing of the present graft polymer has been overcome in accordance with the invention by blending of the graft polymer with a small proportion of a monoalkenyl arene-alkadiene hydrocarbon block thermoplastic elastomer (typified by a block copolymer of styrene and 1,3-butadiene or isoprene) more fully described hereinafter. The prior art does not disclose or suggest awareness of the above-described ageing problem associated with the present vinyl halide-graft-hydrocarbon polyolefin polymers or teach or suggest that this problem is overcome by incorporation of the aforementioned block elastomers in the graft polymer.
U.S. Pat. No. 4,048,254, (E. L. Hillier et al., issued Sept. 13, 1977) discloses polymer mixtures containing two block radial elastomers of 1,3-butadiene and styrene having different diene contents together with 5 to 75% (based on the weight of the block polymers) of certain other polymers, namely epoxide polymers, acrylic polymers, styrene-acrylonitrile polymers, polycarbonates, polyolefins, polystyrenes, polyvinyl chloride, olefin/polyvinyl chloride copolymers, preferably polyether-and polyester-urethane polymers, methyl methacrylate-styrene-1,3-butadiene copolymers, and methyl methacrylate-acrylonitrile-styrene-1,3-butadiene copolymers, as well as mixtures thereof. The reference compositions have a sufficient clarity, hardness, tensile strength and elongation to render them suitable for use in medicinal applications particularly as a replacement for vinyl halide polymers. This reference does not disclose a particular combination of a vinyl halide polymer or copolymer with the block polymers or relate to compositions having an improvement in impact resistance (especially in sub-ambient temperature impact resistance on ageing of the composition). It is particularly emphasized that the reference disclosure relating to vinyl halide polymers and copolymers thereof with olefins is not descriptive or suggestive of the present graft polymers which are highly distinctive from conventional vinyl halide polymers and copolymers in their properties (especially their low temperature impact properties). Accordingly, this reference does not teach or suggest the present invention.
U.S. Pat. No. 4,048,255, (E. L. Hillier et al., issued Sept. 13, 1977) discloses a nonclear mixture of two radial block copolymers of 1,3-butadiene and styrene having different diene contents with 3-75% (based on the weight of the block polymers) of another polymeric material namely polyolefin-butyl rubber graft copolymers, chlorinated polyethylene, styrene-olefin block copolymers, polyether urethane elastomers, polyisobutylene and mixtures thereof. The reference mixtures have sufficient elasticity and resealability to be employed as pharmaceutical sealing compositions. The polymers which are employed by the reference as substrates for the block polymer additives do not include or suggest the present vinyl halide graft polymers. The physical properties of the reference compositions do not include or suggest impact resistance properties especially enhancement of low temperature impact resistance on ageing. Accordingly, this reference also does not teach or suggest the present invention.
U.S. Pat. No. 3,366,709, (M. Baer, issued Jan. 30, 1968) is directed to graft polymers of vinyl halide upon a trunk polymer which is a copolymer of a monoolefin such as ethylene or isobutylene and vinylidene chloride. The reference vinyl halide-graft polyvinylidene chloride/olefin polymers are prepared by bulk, solution emulsion or preferably suspension polymerization and have an enhanced impact resistance at sub-ambient temperatures compared to mechanical blends of ungrafted polyvinyl halide and the vinylidene chloride-olefin copolymer. The reference graft polymer is distinctive from the present graft polymer since the trunk polymer component of the present graft polymer is a hydrocarbon whereas the reference trunk polymer, by virtue of its vinylidene chloride monomer residues, is substituted with chlorine. Moreover at Example VI (Col. 3) the reference teaches against use of a vinyl halide-graft-hydrocarbon polyolefin polymer as a graft polymer component of the reference composition. Accordingly, the reference graft polymer is distinctive in structure and properties from the hydrocarbon trunk polymer-containing graft polymer of the invention. At Col. 1, lines 19-30, the reference discusses unsatisfactory prior art attempts to improve the low temperature impact resistant properties of conventional, i.e. ungrafted, vinyl halide polymers mentioning that it is known to mechanically blend the vinyl halide polymer with polymeric materials, inter alia, butadiene-styrene polymers. As pointed out by the reference at Col. 1, line 28, the prior art use of such polymer additives only improved low temperature impact strength of vinyl halide resins by sacrifice of another desirable physical property, such as high heat distortion temperature. This reference disclosure is not seen to suggest the present block polymers which, as explained below, are highly distinctive structurally from well-known randomly polymerized butadiene-styrene copolymers, e.g. conventional styrene-butadiene rubber, and possess, as a result, highly distinctive properties such as self vulcanization (i.e. exhibition of vulcanization properties without vulcanization-produced chemical cross linkages) over the conventional styrene-butadiene elastomers. While the reference, at Col. 5, lines 60-66, lists a number of polymeric additives which may desirably be mechanically blended with the reference graft polymer composition, the list does not include the aforementioned styrene-butadiene polymer additive mentioned in Col. 1. The reference, it is noted, nowhere alludes to the problem of loss of low temperature impact resistance of vinyl halide-hydrocarbon polyolefin graft polymers on ageing. Since the reference does not teach or suggest the present graft polymer or the present block polymer additive, it does not teach or suggest the invention. In teaching away from the present types of vinyl halide graft polymer (i.e. from one derived from hydrocarbon polyolefin trunk polymers) and from copolymers of styrene and butadiene in general as additives for polyvinyl halide resins, in general, the reference is, moreover, seen to teach away from the invention.
N. Platzer, Chemtech, October 1977, pages 364-641 discloses the use of the present block thermoplastic elastomers as components for enhancing the impact resistance of high impact polystyrene and acrylonitrile-1,3-butadiene-styrene copolymers. Also it is known to employ these block polymers as impact modifiers in polyethylene and polypropylene. As is apparent by comparison of Examples 1-3 with Control Example 4 of this application, the block polymer additive, prior to ageing, lowers the low temperature impact resistance of the vinyl halide graft polymer in which it is incorporated so that the block polymer would not be regarded as a low temperature impact modifier for the present graft polymers. Hence, the prior art disclosure of the present block polymers as impact modifiers for the foregoing non-vinyl halide resins does not teach or suggest the invention.